The present invention relates to a Raman spectroanalyzer, and more particularly to a laser Raman microprobe which enables analysis of a fine sample.
The laser Raman microprobe is disclosed, for example, in U.S. Pat. No. 4,195,930 to Delhaye et al. In this device, a laser beam generated by a laser oscillator is irradiated to a sample through a microscope and a light applied to the microscope, of a Raman scattered light emanated from the sample and a reflected laser beam from the sample is split by a splitting prism. One of the two split components is directed to a screen to display an enlarged image of the sample on the screen. The other component is directed to a double monochromator where it is analyzed, and the light is applied to a photomultiplier to convert it to an electrical signal. By recording and reading the electrical signal, the sample is quantatively and qualitatively analyzed.
In this device, in order to perpendicularly irradiate the sample by the laser beam, a ring-shaped mirror or a disc-shaped half-mirror is arranged in the microscope. When the ring-shaped mirror is used a fine sample such as several tens microns or several microns in diameter cannot be analyzed because a condensed laser beam by the microscope is several hundreds microns in diameter. On the other hand, when the disc-shaped half-mirror is used, the condensed laser beam diameter by the microscope is in the order of 1 micron and a sample larger than 1 micron in diameter can be analyzed. However, when the half-mirror is used, the Raman scattered light from the sample is reduced to one half by the half-mirror and further reduced to one half by the splitting prism and hence the analysis sensitivity is lowered. In addition, since the Raman scattered light as well as the reflected laser beam is applied to the double-monochromator, the reflected laser beam must be removed by the double-monochromator and the device is of large scale and expensive.